The invention relates to liquid flotation separation components, Systems and methods. More particularly, the present invention relates to liquid conditioning components, systems and methods that treat livestock waste to remove contaminants such as nitrates and microbes from carrier water streams such as barn or yard wash water.
Livestock operations produce waste in the form of manure and urine. For the purpose of this application, the term xe2x80x9cfeedlotxe2x80x9d means confined animal or milk production operations in areas that produce no forage. In 1992, the USDA estimated the number of feedlots at 510,000. In addition, there are over 1,000 dairies in California alone. The same year, it estimated the total number of animals in operations with over 500 animals at 6.4 million cattle, 29 million hogs, and 744 million chickens. The average dairy cow produces over a cubic foot of waste daily. It is clear that the tonnage of feedlot waste is high.
Current federal regulations prohibit discharge of feedlot wastewater to surface waters unless extreme storms cause overflows from containment systems designed to hold wastewater and runoff. An extreme storm is defined as 24 hours worth of a 25-year storm. Although these regulations have been in place since 1974, risks to the environment and fisheries persist.
Feedlot waste has contaminated aquifers, the air, and surface waters such as streams, rivers, lakes, bays, estuaries and the ocean. For example, the storms that flooded the east coast of the United States in recent years resulted in discharge of millions of gallons of hog and other livestock waste into the Chesapeake Bay and other fisheries.
Composting of livestock waste into useful materials has been practiced for millennia. However, composting of fresh livestock waste in the quantities in which it is produced on a modern feedlot is impractical. This is because aerobic composting will not take place if: 1) the moisture content is above 65%, which most fresh manure or its carrier streams are; 2) the carbon to nitrogen ratio is not kept within a narrow range; 3) adequate oxygen cannot reach into the waste to support the microbes; or 4) the temperature drops below a minimum necessary to sustain the microbe population. Absent large-scale solids mixing equipment, which is rarely employed, the carbon to nitrogen ratio is fixed by the type of livestock and its feed. In addition, some farms screen out the carboniferous solids for reuse. Thus, the ratio is not adjusted to bring it into the compostable range. Airborne oxygen cannot penetrate more than a few inches into piled manure (e.g. windrows), leaving the volume of manure inside this surface layer deficient in oxygen. Temperatures in most livestock raising areas in the continental U.S. fall below 40xc2x0 F. for substantial periods. If pile temperature falls below 55xc2x0 F., microbial activity essential for composting will slow or stop. Thus, direct composting of the entire waste stream in feedlot operations over 300 animals (cattle equivalents) is rarely employed.
Feedlot waste is primarily manure and urine in a carrier stream of water. There is much variability in feedlot waste management. However, most feedlot operations use gravity settling, which removes primarily inorganic constituents from the carrier stream and leaves the organic constituents, followed by some form of biological processing. Usually, the stream passes from settling pits into lagoons, where the organic constituents are food to microbes. Aerobic microbial digestion of the food requires oxygen and results in biomass, heat, carbon dioxide and water according to the following formula:
Food+O2xe2x86x92Biomass+energy (heat)+CO2+water
As bacteria age and die, their cells create biological oxygen demand (BOD) of their own and the dead bacteria become food for the others. As the cycle repeats, more of the biomass is converted to CO2 and water. Consequently, the longer the time period allowed for decomposition, the lower the volume of the resulting sludge.
However, if high enough, as in feedlots, this BOD in the carrier stream of water uses up the dissolved oxygen in the water, eventually killing the aerobic bacteria and changing the environment to one that supports anaerobic bacteria. Anaerobic decomposition produces methane, hydrogen sulfide, ammonia, and CO2. Hydrogen sulfide and the ammonia are odorous and toxic air contaminants. Also, high BOD surface runoff damages downstream receiving waters by, for example, suffocating fish. Therefore, BOD must be substantially reduced before the water leaves the livestock operation.
The technologies aimed at reducing BOD have evolved with concentrations of human population. Manipulation of contact time has evolved as a primary way to treat organic wastewaters. Technologies have moved from unaerated shallow lagoons through mixed and aerated ponds. These methods share the disadvantages of large land area requirements, inefficient aeration, little process control, and the additional biological oxygen demand generated by the algae that tends to grow on the surface. Trickling filters, which repeatedly flow the water to be treated over a media containing air spaces, addressed the land area problem. However, these filters retain the problem of little process control and suffer from freezing in the winter and plugging.
To address the plugging, freezing, large land requirements and inefficient aeration problems, activated sludge systems were developed and are the main technology used today for human waste. These systems mix food, bacteria nutrients and oxygen enough to prevent flotation and settling. Oxygen is dissolved into the liquid by mechanical means. However, the high cost and complexity of these technologies has been a barrier to their use in feedlot operations.
Instead of employing activated sludge systems, the typical 300+ animal California dairy operation flushes stalls with water, screens the water for solids later processed into bedding, employs sedimentation to separate the mineral particles and other materials heavier than water, sends the supernatant to one or more lagoons where microbes convert dissolved solids to suspended solids in the form of more microbes, and land applies the biologically altered water by irrigation, knifing it into the soil or injecting it into the ground.
The liquid that is land applied typically contains high concentrations of nitrate. This is because the age of the sludge in the lagoons and the liquid from the lagoons that is reused as wash water is over seven days old. Feedlot wastewater systems contain large quantities of nitrifying bacteria, which use ammonia as food, because the wastewater is over 5 days old. 
Nitrification increases the BOD of the water. In addition, nitrates are toxic to cattle and humans. Nitrate poisoning in cattle produces spontaneous abortion and death. State and federal regulations prohibit dosing the land with more nitrates than the vegetation grown thereon can take up. This limits the amount of used water that farm operators may dispose of via land application.
U.S. Pat. No. 5,698,110 (Wyatt, et al) addresses animal excrement by filtering the solids, mixing in a lime and cellulose-based deodorizer, and drying. This technology, however, does not address the liquid. Cattle waste averages only 13% solids, the rest being liquid. Thus, the Wyatt invention does not address over xc2xe of the waste stream.
U.S. Pat. No. 5,472,472 (Northrup) addresses animal excrement by precipitating solids in a reactor, passing the slurry to a bioreactor where it is aerobically and anaerobically treated, and then to a constructed wetland. It claims to treat the water to a generally nutrient-free discharge that can be used for irrigation. The system requires aerators, mixing of metallic salts to precipitate phosphorous, a pond with aerobic, anaerobic and facultative bacteria, and a wetland divided into cells as the last step. This requires a large land area, has little process control, and is complex. As such, it retains several of the main disadvantages of established technologies.
Waste and process water treatment in non-farm operations frequently involves adding polymeric materials to the stream. Polymers are long chain molecules. This aspect makes them effective at joining with contaminants in the stream to ferry them out. Unfortunately, the long molecular chain nature of polymer molecules results in molecular damage under established high shear mixing methods. Damaged polymer molecules usually do not function as well, necessitating increases in dosage. As dosage increases, polymer usage, and hence cost, are increased. Away is needed to add polymers to liquid streams without damaging the polymers. In addition, polymer molecule charges tend to be xe2x80x9cself-satisfyingxe2x80x9d, which means that positive charges at one site tend to pair with negative charges elsewhere along the length. This causes the polymer molecule to twist into a knot. In this coiled form, the charge sites of the polymer molecule are much less available for connecting with contaminants in the stream and the polymer is less effective, again necessitating higher dosing. Established methods for uncoiling polymers include pH adjustment. A non-chemical method to accomplish the same thing would reduce or obviate the need for pH-adjusting chemicals.
Established mixing methods do not fully uncoil polymeric additives, leaving charge sites unavailable to contaminants in the stream. Thus, in order to optimize the performance of polymers and minimize their dosages, a method is needed of delivering them to the stream in a state where the number of charged sites available to the water is maximized without damaging the molecules.
The solids component of feedlot waste contains a substantial proportion of salt, averaging between 4% and 9%. Salt increases the electroconductivity of soil, makes the soil less productive, and is a source of leachable salts to surface waters. Such salt is dissolved rather than suspended, and so cannot be addressed as a particulate. This severely limits the options for salt reduction. Currently, no salt removal technology is accepted in the feedlot industry.
Salt can be addressed through osmosis, in particular, using osmotic membranes. However, such membranes xe2x80x9cblindxe2x80x9d or are clogged by suspended solids and microbial enzymes, which are abundant in feedlot waste streams. Polymeric coagulants and flocculants, which can remove suspended solids, also tend to blind these membranes. These practical problems have prevented osmosis from being used to reduce salt load in feedlot waste.
Accordingly, there is a need for an ecologically suitable means for managing animal waste that minimizes or eliminates the disadvantages of the prior art, including insufficient process control, large land area requirements, complexity, and anaerobic digestion byproducts (odor, toxic air contaminants). What is also needed is an improved process for the biological transformation of animal wastes into useful materials. What is further needed is a process that efficiently delivers surface chemistry that reduces the BOD of feedlot wastewater. The present invention fulfills these needs, and provides other related advantages.
The treatment method and system of the present invention provides an efficient and cost-effective way of treating feedlot wastewater streams by reducing the biological oxygen demand (BOD). This is accomplished by reducing the nutrient concentration to a level at which microbes can convert the remaining nutrients quickly to innocuous or useful byproducts. The system employs a hydrocyclone to aerate wastewater and maximize particle-bubble contact, followed by flotation to separate particles and nutrients from the stream. The system is designed to work with existing installed treatment equipment, allow real time process control and be simple to operate. It is inserted into the existing waste handling loop after screening and settling and before the first lagoon.
The treatment method generally comprises the steps of first screening coarse solids from the feedlot wastewater. Coarse solids are those any of whose dimensions exceed the smallest dimension of the aperture in the hydrocyclone head. Inorganic undissolved solids are then removed from the screen wastewater. Bubble-particle aggregates are created by directing the wastewater into an inlet of a hydrocyclone. The wastewater is then channeled from an outlet of the hydrocyclone to a separation tank. The bubble-particle aggregates are separated from the wastewater by allowing the bubble-particle aggregates to rise and accumulate on a free liquid surface of the tank, and the wastewater to settle below the bubble-particle aggregates. The bubble-particles are then removed from the tank, and the treated wastewater transferred to a holding reservoir lagoon. If desired, salts may be removed from the wastewater by filtering the wastewater through salt-removing filters before the treated wastewater is transferred to the reservoir lagoon. Water from the lagoon may be reused as irrigation or barn flush water.
Addition of chemicals may be required to enhance formation of flocs for flotation. A flocculent and/or a coagulant is added to the wastewater either upstream of the hydrocyclone or into the hydrocyclone. The pH of the wastewater stream may require adjustment to minimize the quantity of polymer needed and also to optimize the performance of the polymer. Thus, a pH adjusting chemical is often added to the wastewater upstream any coagulants or floculants.
The bubble-particle aggregate creation and separation steps can be accomplished using various systems. In its simplest form, the stream of wastewater is directed through the hydrocyclone and channeled into a separation tank. Bubble-particle aggregates are allowed to accumulate at a free liquid surface of the tank, while the treated wastewater is removed from the tank to a reservoir lagoon.
In a second embodiment, referred to as a small footprint embodiment, the hydrocyclone defines a first chamber. The hydrocyclone is configured to pass the wastewater through an inlet thereof to an outlet thereof in a generally helical manner to create the bubble-particle aggregates. A second chamber peripherally surrounds the outlet of the hydrocyclone so as to be in fluid communication therewith. The second chamber has a generally upwardly directed outlet. A third chamber peripherally surrounds the outlet of the second chamber so as to be in fluid communication therewith. The third chamber has a generally downwardly directed outlet. A fourth chamber defined by the separation tank peripherally surrounds the outlet of the third chamber so as to be in fluid communication therewith. The bubble-particle aggregates float to the surface of the tank where they are removed. The tank includes an outlet disposed below a liquid surface thereof for transferring the treated wastewater to the reservoir lagoon.
A third embodiment, referred to as a non-space-limited embodiment, includes the hydrocyclone configured to pass the wastewater through an inlet thereof to an outlet thereof in a generally helical manner to create the bubble-particle aggregates. First and second pits are in alternate fluid communication with the outlet of the hydrocyclone and alternatively serve as a receiving pit when receiving wastewater from the hydrocyclone, and a quiescent separation pit when not receiving wastewater from the hydrocyclone. Each pit has an outlet, which can be selectively opened for transferring the separated liquid from the pit to the reservoir when the pit is in its quiescent state. Means are also provided for removing the bubble-particle aggregates from the quiescent pit.
In a fourth embodiment, referred to as a vaned tank embodiment, the hydrocyclone, which is configured to pass the wastewater therethrough in a generally helical manner to create the bubble-particle aggregates, is in fluid communication with a separation tank. The outlet of the hydrocyclone is typically immersed within liquid of the separation tank. The tank includes a plurality of vanes arranged to facilitate the separation of the treated water from the bubble-particle aggregates by directing the bubble-particle aggregates to a free liquid surface of the tank, while channeling treated wastewater below the vanes. Preferably, the tank includes a downwardly directed ramp below the outlet of the hydrocyclone and a baffle spaced from the ramp to direct the wastewater from the hydrocyclone outlet below the vanes within the tank. An outlet is disposed in the tank below the free liquid surface thereof for transferring the treated wastewater to the reservoir.
By removing fecal and urine particles before they are converted to nitrate and nitrite by nitrifying bacteria, the invention allows the water to carry a lower load of nutrients and thus a lower BOD to the lagoon. The lower load of nutrients supports a smaller population of microbes per unit volume, which prevents build up in the lagoon of both toxic levels of the products of bacterial digestion and algae. The BOD of the water stays low enough to prevent the dissolved oxygen in the water from being used up and transitioning into anaerobic conditions. Windborne microbes populate the lagoon and convert dissolved solids (nutrients) into suspended solids (microbial cells), which are removed as particles during the next pass as wash water through the invention. This water can be used as irrigation water or reused as wash water.
Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.